Although infants who cry or fuss excessively are frequently referred to pediatricians, medical research has yet to confirm whether these features represent a clinical syndrome linked to a compromised outcome or reflect normal development. To answer this question, the proposed longitudinal research study identifies excessively crying infants and uses laboratory-based experimental procedures to evaluate autonomic regulation at 6, 12, and 24 months of age. The study contrasts the developmental profile of infants classifiec nto four groups based on excessive crying and the age at which excessive crying resolves. This longitudinal design evaluates whether autonomic regulation, excessive crying and the age that excessive crying resolves during infancy are predictive indices of developmental outcome. The proposed research focuses on the following aims: 1) to evaluate whether the autonomic response at 6-months of age distinguishes among the crying groups;2) to evaluate whether excessive crying and age at which excessive crying resolves (i.e., group classification) is related to developmental outcome at 12 and 24 months;and 3) to evaluate whether the autonomic response profile at 6- and 12-months, with or without the behavioral feature of excessive crying, is a marker for a compromised developmental outcome at 24 months. Relevance to public health: Since pediatricians, early intervention specialists, and health care providers do not know whether excessive crying is independent of developmental outcome or a lead indicator of developmental delay, they are limited in their management of these early behavioral features. If, however, these infants are at risk for a compromised development and/or the measurement of autonomic reactivity refines this measure of risk, then early knowledge of this risk will be useful in developmental assessment procedures, management and treatment models.